Derivative Instruments and Hedging Activities - Effect of Interest Rate Swaps on Statement of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
5 year interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate swaps reclassified to earnings	$ 56	$ 108
10 year interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate swaps reclassified to earnings	8	59
Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate swaps reclassified to earnings	$ 64	$ 167

The amount of net gains or losses on interest rate cash flow hedges reclassified during the period to earnings from accumulated other comprehensive income upon the hedged transaction affecting earnings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Name:	us-gaap_InterestRateCashFlowHedgeGainLossReclassifiedToEarningsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration